Maleated nanolignin as a new coupling agent for wood-plastic composites

In this work, the influence of maleic anhydride-treated nanolignin as a coupling agent on the various properties of wood fiber-polypropylene composites was investigated. For this purpose, extracted lignin from Bagasse Soda black liquor was modified with maleic anhydride and then different ratios of unmodified and modified nanolignin (1, 3 and 5 wt%) were added to the wood fiber-polypropylene mixture. The composites were then manufactured by injection molding after mixing mechanically to the wood flour either virgin or maleated nanolignin and polypropylene. Structural and thermal properties of nanolignin after modification by maleic anhydride along with physical and mechanical properties of the manufactured composites were determined according to standard methods. The FTIR analysis indicated nanolignin rearrangements showing that some bonds changed or formed after its modification with maleic anhydride. The glass transition temperature of the nanolignin decreased by esterification from 130°C to 100°C. The panel testing results indicated that all physical and mechanical properties of the composites were continuously improved by increasing the maleated nanolignin content from 1 to 5wt%. Thus, the composites with maleated nanolignin presented higher dimensional stability and mechanical strength compared to those prepared with unmodified nanolignin. Scanning electron microscopy (SEM) showed that treatment with maleic anhydride improves the uniform dispersion of nanolignin in the polymer matrix. The manufactured WPCs can be used as interior and exterior building materials such as decks, sidings and etc.